In connection with a conventional variable intake device, Japanese Patent Laying-Open No. 2002-276380, for example, discloses a variable intake device directed to improving the mountability to a V-type internal combustion engine in an engine room. The variable intake device disclosed in Japanese Patent Laying-Open No. 2002-276380 has a short-circuit pipe communicating with a first surge tank during the path of an intake manifold. A valve to open/close the short-circuit pipe is provided in the path of the pipe.
Further, Japanese Patent Laying-Open No. 10-299594 discloses a method of attaching a variable intake valve in order to ensure the accuracy of the flow. The variable intake valve disclosed in Japanese Patent Laying-Open No. 10-299594 establishes communication between a surge tank chamber and an intake pipe. A valve body constituting the variable intake valve is provided with a rotatable flat valve plug connected to a valve shaft.
As disclosed in the aforementioned Japanese Patent Laying-Open Nos. 2002-276380 and 10-299594, a variable intake device is provided with a short-circuit pipe shunting between a surge tank and an intake pipe. A valve to control the air flow within the pipe is arranged in the short-circuit pipe. The air flow in the short-circuit pipe is cut off by closing the valve, forming a relatively long intake path corresponding to the intake pipe.
When the valve is open, air flow within the short-circuit pipe is allowed, forming a relatively short intake path shunting between the surge tank and the intake pipe. In order to minimize the pressure loss at the site where the valve is located, the valve is open parallel to the streamline of the air flow within the short-circuit pipe. If a smooth connection is not established between the short-circuit pipe and the intake pipe, air cannot merge smoothly from the short-circuit pipe into the intake pipe. Deviation of the air flow will occur, leading to the possibility of increasing pressure loss.